Since 2001, governments in Canada and the United Kingdom appear to have increasingly sought to use secret evidence in proceedings against individuals suspected of posing a security threat, relying on the courts to review and legitimate executive claims in closed proceedings. Yet, in the face of secret evidence, adjudicative decision-making is subject to several extraordinary weaknesses. First, the judge is precluded from hearing additional information that can come to light only if the individual or the public is aware of the executive’s claims. Secondly, courts are uniquely reliant on the executive to be fair and forthcoming about confidential information and to characterize accurately the case for secrecy. Thirdly, the dynamic or atmosphere of closed proceedings may condition a judge to favour unduly the security interest over priorities of accuracy and fairness. Even where the use of secret evidence is not deemed to be irreparably unsafe or unfair, therefore, its admissibility must be premised on the acknowledgment and careful consideration of corresponding weaknesses in adjudication.